1. Field of the Invention
The present invention relates to a hybrid automatic repeat request (HARQ) method in a wireless access system that supports collaborative transmission and a device using the same.
2. Related Art
M2M Communication (Machine Type Communication: MTC)
A machine-to-machine (M2M) communication (machine type communication, MTC) is described in brief below.
Machine to machine (M2M) communication as it is means communication between electronic devices. That is, M2M communication means communication between things. In general, M2M communication means wired or wireless communication between electronic devices or communication between a device and a machine which are controlled by human beings, but M2M communication is used to specially denote wireless communication between an electronic device and an electronic device, that is, devices. Furthermore, M2M devices used in a cellular network may have lower performance or capability than common terminals.
There are many terminals within a cell, and the terminals may be classified depending on the type, class, service type, etc of the terminal. For example, according to an operation type of terminals, the terminals can be divided into a terminal for human type communication (HTC) and machine type communication (MTC). The MTC may include communication between M2M devices. Herein, the HTC implies a signal transmission/reception operation in which signal transmission is determined by human interventions, and the MTC implies an operation in which each terminal autonomously transmits a signal either periodically or in an event-driven manner without human interventions.
In addition, when machine to machine (M2M) communication (or machine type communication (MTC)) is taken into consideration, the total number of terminals will increase suddenly. M2M devices may have the following features depending on supported service.
1. A large number of terminals within a cell
2. A small amount of data
3. Low transmission frequency (may have periodicity)
4. A limited number of data characteristics
5. Not sensitive to time delay
6. Low mobility or fixed
In addition, the M2M communication can be used in various fields such as secure access and surveillance, tracing and recovery, public safety (emergency situation, disasters), payment (vending machines, ticketing machines, parking meters), healthcare, remote control, smart meters, etc.
Client Cooperation (Collaborative Transmission)
Standardization for a cooperative-MIMO (CO-MIMO) and a signal transmission through a relay or femto cell in an IEEE 802.16m system or LTE (-A) system is in progress to enhance transmission efficiency and throughput of devices with poor channel status among MSs positioned in a cell. Further, besides methods of supporting devices using a base station or a femto cell or relay that operates as a base station as described above, research for client cooperation (CC) that transmits signals through cooperation between devices is recently underway for the 802.16 systems or LTE (-A) systems.
Herein, CC means that a signal is transmitted and received through device-to-device direct communication unlike the aforementioned repeater or femto cell, and the transmitted and received signal is collaboratively transmitted to a device or a base station.
When a source device and a collaborative device collaboratively transmits a signal to the base station in a UL region through collaborative transmission, a signal may be generated, which is used for even the collaborative device that transmits UL data of the source device to the base station to transmit its own UL data to the base station. In this case, the collaborative device needs to receive a resource allocation for transmitting a UL signal from the base station by performing a resource request for transmitting the signal to the base station in order to transmit its own signal during collaborative transmission.
HARQ (Hybrid Automatic Repeat Request)
A technique that increases reliability of wireless communication includes an automatic repeat request (ARQ). In the ARQ, when a receiver fails to receive a data signal, a transmitter retransmits the data signal. Further, the technique also includes a hybrid automatic repeat request (HARQ) acquired by combining a forward error correction (FEC) and the ARQ. A receiver using the HARQ basically attempts error correction for the received data signal and determines retransmission or not by using an error detection code. The error detection code may use a cyclic redundancy check (CRC). When an error of the data signal is not detected through a CRC detection process, the receiver judges that decoding the data signal is succeeded. In this case, the receiver transmits acknowledgement (ACK) signal to the transmitter. When the error of the data signal is detected through the CRC detection process, the receiver judges that decoding the data signal is failed. In this case, the receiver transmits a non-acknowledgement (NACK) signal to the transmitter. When the transmitter receives the NACK signal, the transmitter may retransmit the data signal.
As such, the HARQ is an important technique that increases the reliability of the wireless communication. However, in order to perform the HARQ, when the data signal is transmitted or received or when the HARQ ACK/NACK signal for the data signal is transmitted or received be discussed. Therefore, in the wireless communication system, an efficient HARQ performing method needs to be provided.